THE F, BLEND ACCOMPANIED BY GENIC 

 PUEITY 



A Description of Mechanical Charts for Illustrating 

 Mendelian Heredity in Each of Thkee Well- 

 known Cases of Blending Inheritance in 

 the First Hybrid Generation 



HARRY H. LAUGHLIN 

 Eugenics Record Office, Cold Spring Harbor, N. Y. 



The mechanical charts herewith figured are the first of 

 a series prepared for the purpose of presenting graph- 

 ically and schematically the established facts of heredity. 

 These particular mechanisms, illustrating blending in- 

 heritance, consist essentially of wooden slabs on which the 

 gametic formulae of the several generations are charted 

 — those for F 1 and F 2 are written on flat surfaces, 

 while that for F 1 is inscribed on cylinders which turn 

 freely. A capital letter represents a gene; the corre- 

 sponding small letter the absence of that gene. The lo- 

 cation of genes, whether they lie in the same chromosome 

 i. e., are linked, or in different chromosomes, is shown 

 graphically by placing their symbols in the same or in 

 different squares, or upon the same or different halt- 

 cylinder surfaces. In each of these selected cases the 

 individuals of the P x generation are homozygous in re- 

 spect to both of the traits or allelomorphic phases con- 

 cerned. The genes contributed by the P x generation to 

 the Fj zygote are charted on the starred faces of the 

 freely turning cylinders. The back of each spool contains 

 the same inscription as the face of its partner cylinder. 

 Each face of a cylinder represents a chromosome— the 

 two faces the two chromosome types in reference to the 

 741 



